It is known that a liquid crystalline polyester is a polymer comprising a rigid molecular chain, and highest strength and elastic modulus can be obtained among fibers prepared by melt spinning by highly orienting the molecular chain in the fiber axis direction in the melt spinning and further carrying out solid phase polymerization. Further, it is also known that the liquid crystalline polyester can be improved in thermal resistance and dimensional stability by solid phase polymerization because the molecular weight increases and the melting point elevates by solid phase polymerization (see, for example, Japanese Patent Application Laid-Open Publication No. 2010-209495 (sixth and seventh pages)). Thus, in a liquid crystalline polyester fiber, the high strength, high elastic modulus, and excellent thermal resistance and thermal dimensional stability are exhibited by carrying out solid phase polymerization. A solid-phase polymerization reaction is generally carried out at high temperatures around the melting point. Because of this, fusion bonding between yarns tends to take place. For the purpose of preventing the fusion bonding causing deteriorated characteristics and fibrillation of the yarn, it is an important point of technique in the production of the liquid crystalline polyester fiber to add a solid-phase polymerization oil agent.
Meanwhile, the solid-phase polymerization oil agent remains on the fiber surface after the solid-phase polymerization and in turn accumulates on guides, rollers, or tension providers in post processing steps of fibers, for example, a weaving step, thereby generating waste called scum. Because contamination of this scum into products causes product defects or yarn breakage by increased tension fluctuation, it is also an important point of technique in the production of the liquid crystalline polyester fiber to clean and remove the solid-phase polymerization oil agent after the solid-phase polymerization.
As this solid-phase polymerization oil agent, fluorine-based or silicone-based organic compounds with thermal resistance have been employed thus far. What has been proposed is, for example, utilization of polydimethylsiloxane which is water emulsifiable, easy to applied to the fiber surface and thermal resistable at high temperatures (Japanese Patent Application Laid-Open Publication No. 2010-209495 (sixth and seventh pages) and Japanese Patent Application Laid-Open Publication No. 2010-248681 (eleventh page)). That is, according to Japanese Patent Application Laid-Open Publication No. 2010-209495 (sixth and seventh pages) and Japanese Patent Application Laid-Open Publication No. 2010-248681 (eleventh page), a liquid crystalline polyester fiber exhibiting a very low amount of oil adhesion is obtained by applying polydimethylsiloxane with high thermal resistance as a solid-phase polymerization oil agent and carrying out a cleaning-heat treatment after the solid-phase polymerization.
Further, also known is a technique of utilizing inorganic particles with thermal resistance, instead of the used of the organic compound, as solid-phase polymerization oil agent (Japanese Patent Application Laid-Open Publication No. 2011-168930 (second and eighth pages)).
It was revealed that, because polydimethylsiloxane used in the above method of production described in Japanese Patent Application Laid-Open Publication No. 2010-209495 (sixth and seventh pages) and Japanese Patent Application Laid-Open Publication No. 2010-248681 (eleventh page) caused gelling by cross-linking reaction among polydimethylsiloxane under conditions of the solid-phase polymerization and the gelled product solidly adhered to the fiber surface, polydimethylsiloxane remained on the fiber even after mechanical cleaning such as ultrasonic cleaning in addition to cleaning by surfactants. That is, an amount of oil adhesion in the above documents was calculated from yarn weight (W0) before the cleaning and yarn weight (W1) after the ultrasonic cleaning using the following equation, and it was found that, because the gelled product was not completely dropped off at the time of the ultrasonic cleaning, although the amount of adhesion of a solid-phase polymerization oil agent was calculated as a low value, the gelled product of solid-phase polymerization oil agent whose amount could not be measured as the amount of oil adhesion firmly adhered and remained on the fiber:Amount of oil adhesion (wt %)=(W0−W1)×100/W1.
Due to this, according to the method of production described in Japanese Patent Application Laid-Open Publication No. 2010-209495 (sixth and seventh pages) and Japanese Patent Application Laid-Open Publication No. 2010-248681 (eleventh page), a yarn hold very low amount of oil adhesion by strengthening the cleaning in the cleaning step after the solid-phase polymerization. In addition, although, in Examples, effects of suppressing generation of scum and contamination of the scum into the product were confirmed in a weaving step in which a small amount of liquid crystalline polyester fiber was picked to weave as welf, a very small amount of scum was generated, and when extended evaluation was carried out, it was revealed that tension fluctuation by accumulation of the gelled product onto guides, tension providers or the like increased with time; and yarn breakage or contamination of the scum into the product occurred.
Further, in Japanese Patent Application Laid-Open Publication No. 2011-168930 (second and eighth pages), a fiber is applied with swelling clay minerals having properties of swelling and dispersing in water and subjected to solid-phase polymerization. The fiber is immersed in water after the solid-phase polymerization, which enabled dropping solid-phase polymerization oil agent.
However, when such inorganic particles are solely applied on the fiber, or dispersed in a common spinning oil agent or the like and then applied on the fiber, the inorganic particles were firmly adhered on the fiber surface after the solid-phase polymerization step. Thus, similarly to the above examples of polydimethylsiloxane, although the fiber had a very small amount of oil adhesion after the cleaning, the inorganic particles dropped off by being scratched by guides or tension providers in the weaving step, which caused occurrence of tension fluctuations or product defects by product contamination.
As mentioned above, a solid-phase polymerization oil agent for the liquid crystalline polyester fiber that has both effects of suppressing fusion bonding and excellent cleaning properties has not been developed thus far. Thus, a liquid crystalline polyester fiber that is industrially utilizable with suppressed scum generation and tension fluctuation in the weaving step, and is excellent in process passability and product yield; and production technique thereof have not been proposed. The development thereof has been wanted.
It could therefore be helpful to provide a liquid crystalline polyester fiber that has a small amount of deposit (scum) in the weaving step, small fluctuation of running tension, and is excellent in process passability and product yield in the weaving step; as well as a method of production thereof and a mesh woven fabric thereof.